The present invention relates to a bearing assembly, especially for an axially compact miniature motor or ventilator, comprising: a central drive motor mounted through a flange and a bearing support tube, and a rotor bottom secured to the rotor of the drive motor; a friction bearing unit for the (rotary) shaft of the drive motor; and a housing forming a flow passage.
In miniature motors or ventilators, ball bearings or friction bearings are used for rotatably mounting the shaft of the motor. For example, laid-open European application No. 0 100 078 describes an axial ventilator (or blower) which includes a pair of ball bearings for rotatably mounting the shaft of the drive motor, which shaft, in turn, is connected to ventilator blades through a rotor bottom (or head). Mounting of the shaft by means of such ball bearings offers the advantage of high stability of speed of rotation of the thus equipped axial ventilator.
Friction bearings for electric motors and specifically for ventilators are described, for example, in German Pat. No. 20 16 802, U.S. Pat. No. 3,387,153 and laid-open German patent appln. No. 34 17 127.
More particularly, German Pat. No. 20 16 802 shows a bearing assembly in which one annular groove each is provided in the wall of the bore (hole) of a bearing support section and in the peripheral surface of a bearing bush, which grooves are aligned with each other and have inserted therein a radially resilient locking or arresting member, the width of which provides for axial play or clearance between the bearing bush and the support section. However, it is relatively difficult to manufacture a bearing assembly of this type, since one groove each must be machined in both the support section and the bearing bush. This is undesirable from a production aspect because of the extra machining step required for forming these grooves.
Further, in the bearing assembly as disclosed in U.S. Pat. No. 3,387,153, the bearing bush likewise has grooves in its outer peripheral surface, which grooves receive O-rings for sealing the lubricant. In this conventional bearing assembly, the friction bearing unit proper is formed of two parts which are biased against a counter ring connected to the rotor by a spring ring attached to the end of the shaft. This conventional bearing assembly is expensive to manufacture because of the additional grooves formed in the two friction bearing parts. Further, assembling of this bearing assembly is difficult because of, the multi-piece construction of the friction bearing.
Finally, the miniature ventilator as disclosed in laid-open German patent appln. No. 34 17 127 employs a stepped sintered body, received in a mounting tube having end faces which correspond to the steps of the sintered body. The sintered body is secured at the steps of the mounting tube by an intermediate member for which a resilient spacer element may be used, if desired. In this conventional miniature ventilator, the shoulders of the sintered body must be precisely aligned in position with the steps of the mounting tube, and this arrangement also may involve problems in production.
Although sintered bearings are inferior with respect to stability of speed of rotation, they are preferable with respect to noise generation.
Thus, depending on the desired application, with otherwise identical structure, and motors or ventilators are provided, expediently, with sintered bearings or ball bearings. If high stability of speed of rotation is desired, ball bearings are preferable. On the other hand, when the motor or ventilator is desired to operate in a particularly noise-free manner, a sintered bearing is more expedient.
Even if a user normally does not replace the bearing means in a motor or ventilator, nevertheless, it would mean a significant advantage for the manufacturer if the bearing means of a motor or ventilator can be configured so that this motor or ventilator may be equipped with a ball bearing or alternatively with a friction bearing. Accordingly, a motor or ventilator being compatible for equipment with a friction bearing or a ball bearing would be highly beneficial.
Therefore, it is the object of the present invention to provide for an axially compact miniature motor or ventilator, a bearing assembly which permits the use of a friction bearing including a friction bearing unit that may be easily produced, and wherein said friction bearing may be replaced by a ball bearing without any problem.
In a bearing assembly for an axially compact miniature motor or ventilator having a central drive motor mounted through a flange, a bearing support tube, and a rotor of the drive motor with a friction bearing for the shaft of the drive motor, according to the invention, this object is solved in that the friction bearing unit is clamped between a first shoulder of the bearing support tube on the one hand, and a second shoulder of a closure element cooperating with the bearing support tube on the other hand.
Thus, in the bearing assembly according to the invention, the friction bearing unit is disposed, on the one hand, between a first shoulder of the bearing support tube, which shoulder may be formed, for example, by an inwardly protruding projection on the rotor bottom-side end of the bearing support tube, and, on the other hand, a second shoulder which acts upon the end of the friction bearing unit opposite from the rotor bottom and which comprises the closure element cooperating with the bearing support tube.
In a highly advantageous manner, the bearing assembly may be used, for example, in an especially axially compact miniature ventilator for cooling electrical components.
In this way the friction bearing unit does not require any grooves, and rings received in such grooves, for fixing within the miniature motor or ventilator, and, further, may be replaced by a ball bearing without any major modification. Instead of the friction bearing unit, there are provided between the two shoulders a pair of ball bearings separated from each other by e.g. a spacer sleeve.
In a further embodiment of the invention, the closure element is a bayonet-type closure element. This provides for particularly time-saving assembling of the bearing assembly. The bearing support tube, optionally a first rubber ring, a plastic sleeve, a second rubber ring and, then, the friction bearing unit which is thereafter clamped by means of the bayonet-type closure element between the shoulder of the latter and the shoulder of the bearing support tube are sequentially slid onto the shaft.
According to another embodiment of the invention, a sleeve, formed preferably of plastics material, is provided between the first shoulder and a rim of the friction bearing unit, which contacts or abuts the second shoulder. In addition, a rubber ring may be provided between the first shoulder and the sleeve, and between the sleeve and the rim.
Even without such rubber rings, an elastic mounting, and not a rigid press fit is present.
Furthermore, it is advantageous that between the first shoulder and a rim of the friction bearing unit, contacting the second shoulder, there is provided a sleeve formed of an elastic material, for example, rubber. In this way, the sintered body of the friction bearing unit may be formed thinner. This means that said sintered body may be press-shaped. In this way, it is possible to provide a recess in the contact surface of the shaft within the bore (hole) of the sintered body, whereby the contact surface area is reduced.
The sleeve formed of the elastic material may be clamped in the axial direction between the first shoulder and the rim. Preferably, the first shoulder comprises an inwardly extending radial thickened portion of the bearing support tube. In the axial direction, the sleeve formed of the elastic material may extend up to the end of the thickened portion directed away from the first shoulder, or beyond said end. In the radial direction, the sleeve formed of the elastic material is disposed between the bearing support tube and the friction bearing unit.
Also, according to another embodiment of the invention a further rubber ring and a plastic sleeve are provided between the first shoulder and a rim of the friction bearing unit, which rim contacts or abuts the second shoulder with the interposition of a rubber ring. Such a construction is preferable, especially when two separate ball bearings are installed instead of one double-row ball bearing.
Finally, it is also advantageous that a circuit board is connected to the bearing support tube through an insulating piece. This structure offers expedient facility for housing the necessary electrical components within the miniature ventilator.
These and other objects, feature, and advantages of the present invention will become more apparent from the following description when taken in connection with the accompanying drawings which show, for the purposes of illustration only, plural embodiments in accordance with the present invention, and wherein:
FIG. 1 shows a sectional view of a first exemplary embodiment of the bearing assembly for a miniature ventilator;
FIG. 2 shows in the right and left halves thereof, a sectional view of a second and a third, particularly advantageous exemplary embodiment, respectively, of the bearing assembly according to the invention;
FIG. 3 is a sectional view of a fourth (exemplary) embodiment of the bearing assembly, including a (printed) wiring board connected to the bearing support tube; and
FIGS. 4 and 5 are each a sectional view of a fifth and a sixth embodiment, respectively, similar to the third embodiment.